First slide

Ray optics

Question

A ray of red light is incident on the surface of a slab of glass at an angle of incidence of i. The angle of deviation in the slab is found to be $δ_{r}$ . When a ray of violet light is incident on the same slab of glass at same angle of incidence i, the angle of deviation inside the slab is found to be $δ$ . Then

Moderate

A

$δ_{v} < δ_{r}$
B

$δ_{v} > δ_{r}$
C

$δ_{v} = δ_{r}$
D

information is not sufficient to find the angle of deviation $δ$ .

Solution

Refraction index $(μ)$ of glass changes with wavelength of light according to the graph shown in figure. Since $λ_{v} < λ_{r}$ , from the graph it is clear that $μ_{v} > μ_{r}$ .
By Snell's law, $\sin r = \frac{\sin i}{μ}$ . Therefore $r_{v} < r_{r}$
Also since $δ =$ Angle of deviation $= (i - r)$ , we can conclude, $δ_{v} > δ_{r}$ .

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